106 



fusion, accompanied by more or less extravasation, readily de- 

 velops in such a series all the complexity observed. There are 

 but few outcrops on the line of this stratified belt in Melrose, 

 east of the Boston and Maine R.R., but west of this railroad 

 the series is well developed and the exposures are good. This 

 locality places beyond question the fact that there is a gradual 

 transition between the quartzite and petrosilex, and that por- 

 tions of the latter rock are intercalated in the stratified group. 

 The stratified group at this point is evidently a continuation, 

 under different conditions, of the unstratified diorite on the 

 west. The narrow strip of stratified rocks south of the granite 

 in Melrose consists of a finely stratified gneiss with thin part- 

 ings of mica in minute scales. 



The locality affording at once the greatest variety, and the 

 finest and most instructive exposures, of the stratified rocks is 

 in the north part of Reading. As shown on the map, the vil- 

 lage of Reading is underlaid by coarse eruptive granite ; this 

 extends a short distance north of the village, where it is met 

 abruptly by quartzites, and fine-grained, slaty, hornblendic 

 rocks beautifully stratified. Succeeding these are many alter- 

 nations of quartzite, felsite, diorite, and gneiss, all conform- 

 ably inter stratified, and dipping steeply to the north-west, save 

 where, as is not infrequently the case, the strata are contorted 

 and twisted ; the disturbance being so great in some instances 

 as to obliterate all traces of the bedding. The diorite presents 

 every variety of texture and composition, but rarely contains 

 much quartz; i.e., it seldom passes into well-marked gneiss. 

 Occasional layers are decidedly epidotic, and the rock as a 

 whole is very hornblendic, frequently appearing as a nearly 

 pure hornblende rock. The bedding is fine and even. The 

 petrosilicious strata have commonly the aspect of felsite rather 

 than petrosilex. They are sometimes crystalline or porphyritic, 

 and are usually marked by lines of bedding ; and it is interest- 

 ing to observe that these structure lines, which here no one, 

 probably, would question as indicating sedimentation, are ex- 

 ceedingly like the ordinary banding of the petrosilex ; more- 



